A sensitive and simple modified zeolitic carbon paste electrode for indirect voltammetric determination of nitrate

Carbon paste electrode (CPE) was modified and used for indirect determination of nitrate in aqueous solution based on the decrease in the peak current of Fe(II) redox system in the presence of nitrate. The modification of CPE was done by Fe(II)-exchanged clinoptilolite nanoparticles (Fe(II)-NClin). The electrochemical impedance spectroscopy (EIS) results showed the best charge transfer for Fe(II)-NClin/CPE with respect to raw CPE and the modified CPE with the raw NClin sample (NClin/CPE). To study the effects of more influencing experimental variables (such as modifier%, solution pH, and step potential and amplitude) in square wave voltammetry and reducing the numbers of experiments, experimental design was applied by response surface methodology (RSM). The optimal run was obtained at pH 3.35, amplitude = 335 mV, modifier% = 15, and step potential = 25 mV. Under optimum conditions, the current response of Fe(II)-NClin/CPE was inversely proportional to NO3 (-) in the concentration range from 80 to 1100 mu mol L-1 of nitrate ions with a detection limit of 5.4 +/- 0.2 mu mol L-1 and quantization limit of 18.1 +/- 0.3 mu mol L-1 nitrate. The proposed electrode has a good sensitivity to nitrate anions about 90 nA (mu mol/L)(-1) nitrate (1.5 nA mu g(-1) nitrate). The proposed electrode showed good capability for determination of nitrate in water and meat products as real samples.